Most modern vehicles are equipped with electronic devices such as a keyless remote entry system, transmitters for garage door openers, radios, position navigation systems, etc., each of which requires an antenna system. Such antenna systems in known automotive applications require compromise in the size of the antenna because of space considerations. The effectiveness of the device that utilizes the antenna is decreased when space restrictions limit the size of the antenna. Further, an automotive vehicle body typically has metal at or near the locations of the antenna, which reduces the effectiveness of the antenna. Because of the space restrictions, transmitters that are used to supply radio frequency signals received by the antenna, such as a remote keyless entry transmitter signal, must be relatively large in size and expensive to manufacture because of the need for the transmitter to provide a powerful radio frequency signal. Similarly, receivers with normal power that are associated with antenna systems of reduced size heretofore have not been able to receive a signal until the transmitter is moved very close to the vehicle.
It would be desirable to eliminate or to reduce these restrictions on the transmitter. Prior art devices, however, do not permit the use of a high efficiency antenna that would make it possible to reduce the transmitter signal power. A relatively large antenna in known antenna systems, furthermore, would not be practical from a commercial standpoint because of aesthetic considerations and because of space limitations on integrating the antenna with passenger compartment components. Space limitations are imposed on the antenna system also by the proximity of structural metal in the passenger compartment.